This application claims the benefit of Korean Application No. 2001-55921, filed Sep. 11, 2001, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a key switch of a keyboard unit used as an input device for an information processor, and more particularly, to a key switch of a keyboard unit which is slim.
2. Description of the Related Art
FIG. 1 shows an information processor such as a notebook computer or a personal digital assistant (PDA) with a conventional keyboard unit 100 having a plurality of key switches 110 as an information input unit.
Each of the key switches 110, as shown in FIGS. 2 and 3, includes a key cap 111 which receives a pressure from a user""s finger, a cross link 113 which supports and allows the key cap 111 to move up and down above a substrate 115, a contact terminal portion 114 which generates an electrical signal in response to a pressure provided on the substrate 115, and a rubber dome 112 made of an elastic body which elastically supports the key cap 111 thereunder having a contact protrusion 112a at a center of an inner portion of the rubber dome 112. As the key cap 111 is pressed down and lowered, the contact protrusion 112a presses against the contact terminal portion 114.
FIG. 4 shows that as a user presses the key cap 111, the rubber dome 112 under the key cap 111 is pressed and elastically deforms as the contact protrusion 112a contacts the contact terminal portion 114. Upon contact, an electric signal assigned to the key switch 110 is generated. As the force pressing the key cap 111 is removed, the rubber dome 112 is elastically restored and pushes the key cap 111 upward to its original position.
FIG. 5 shows a relationship between the pressure acting on the rubber dome 112 as the key cap 111 is pressed and the amount of deformation of the rubber dome 112 corresponding to the pressure. That is, as the pressure acting on the rubber dome 112 increases, the amount of deformation of the rubber dome 112 also gradually increases. However, as the pressure reaches a predetermined pressure F1, deformation of the rubber dome 112 occurs radically, and the rubber dome 112 sinks even if the pressure is reduced. This is a buckling phenomenon which provides a user with a sense of manipulation and that a sufficient pressure is applied to the key switch 110. That is, as the key cap 111 of the key switch 110 is pressed, the key cap 111 presses the rubber dome 112 and the rubber dome 112 is gradually pressed and deformed. Upon the pressure F1, the buckling phenomenon occurs, and the rubber dome 112 suddenly sinks inward. This phenomenon allows the user to sense that a sufficient pressure has been applied to generate an input signal and provides a buckling phenomenon is necessary for the user to feel the sense of completeness during a manipulation of the corresponding key switch 110.
Recently, there has been an increasing demand for a slimmer information processor requiring a keyboard unit with a reduced height. However, in a conventional key switch structure, height reduction of the key switch has been limited by the installation of the rubber dome structure. For example, with reference to FIG. 3, a typical height of a stroke h1 from the initial position of the contact protrusion 112a to the contact position with the contact terminal portion 114 is 2.4 mm. That is, as the key cap 111 is pressed 2.4 mm, the contact protrusion 112a presses against the contact terminal portion 114 and causes the buckling phenomenon of the rubber dome 112 to provide a sense of manipulation. In order to reduce the height of the key switch 110, the height h2 of the rubber dome 112 can be reduced. However, if the height h2 is too short, the buckling phenomenon is not produced properly. In addition, a restoration force which pushes the key cap 111 to its original position is weakened improperly. Furthermore, if a rubber is used for the rubber dome 112, resistance to a fatigue destruction is lowered significantly as the height h2 is arbitrarily reduced. That is, to sufficiently perform a function of the key switch 110, the rubber dome 112 must endure a load of about 60 gf which is repeated 10,000,000 times or more. However, if the height h2 of the rubber dome 112 is reduced arbitrarily, fatigue destruction of the rubber dome 112 is likely to occur well before the repetition of 10,000,000 strokes.
Accordingly, it is an object of the present invention to provide an improved key switch structure with a decrease in overall height while maintaining a smooth and stable pressing operability.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
To achieve the above and other objects of the present invention, there is provided a key switch of a keyboard comprising a substrate, a contact terminal portion provided on the substrate, a key cap which selectively moves up and down installed above the contact terminal portion, and an elastic body which supports and allows the key cap to elastically move up and down. The elastic body is a band shaped structure and comprises a protruding portion on one side of the elastic body which presses the contact terminal portion as the key cap moves down, end portions which pivot and are supported above the substrate, a central portion which is bulged to contact a bottom surface of the key cap, and curved portions having an opposite curvature to that of the central portion which includes first curved portion disposed between one of the end portions and the central portion, and second curved portion disposed between the other of the end portions and the central portion.
According to another embodiment of the present invention, a key switch of a keyboard comprises a substrate, a key cap which selectively moves up and down installed above the substrate, an elastic body which supports and allows the key cap to elastically move up and down, and a piezoelectric element coating film coated on a surface of the elastic body which generates an electric signal according to a deformation of the elastic body.